1. Field of the Invention
The present invention relates to the field of improving the reliability of a computer or other electronic system. More specifically, the present invention relates to alternating operation of cooling fans to improve reliability of the fans and the system.
2. Description of the Related Art
Computer systems are information handling electronic systems which can be designed to give independent computing power to one user or a plurality of users. Computer systems may be found in many forms including, for example, mainframes, minicomputers, workstations, servers, personal computers, internet terminals, and notebooks. Computer systems include desk top, floor standing, rack mounted, or portable versions. A typical computer system includes at least one system processor, associated memory and control logic, and a number of peripheral devices that provide input and output for the system. Such peripheral devices may include display monitors, keyboards, mouse-type input devices, floppy and hard disk drives, CD-ROM drives, printers, network capability cards, terminal devices, modems, televisions, sound devices, voice recognition devices, electronic pen devices, and mass storage devices such as tape drives, CD-R drives, or DVDs.
Compared to currently manufactured desk top and laptop computers, early computers consumed relatively little power and relied on convective cooling. Convective cooling allows components to dissipate heat through contact with ambient air. However ambient air is not a particularly efficient conductor of heat. Ambient air can become trapped within a computer casing and act as an insulator instead of a conductor. Trapped ambient air acting as an insulator can increase the operating temperature of a computer. Thus, later computers included fans to draw air from the atmosphere and direct the air into the computer enclosure.
Computer systems continue to increase in operating speed and decrease in size. As operating frequencies increase power consumption also increases. Increased power consumption increases heat generated. An increase in heat generated increases operating temperatures, particularly of the central processing unit (cpu). As computer systems decrease in size the heat generated is confined to a smaller space. Therefore, in smaller faster systems such as laptops, more heat is confined to a smaller space. Confining more heat to a smaller space causes much higher surface temperatures of all components, particularly the heat generating components.
Dissipation of heat through convection or other means allows internal components to remain within their normal operating temperature range. For the reasons described in the preceding paragraph, ambient convection is frequently insufficient to provide sufficient cooling. However, air moving across the surface of a component raises the convective heat transfer coefficient for the surface of the component. Increasing the convective heat transfer coefficient for a component increases the heat transfer from the component to the atmosphere and decreases the temperature of the component. Therefore, designers and manufacturers turn to forced convection (also referred to as xe2x80x9cforced air coolingxe2x80x9d) to provide sufficient cooling capacity.
A cpu consumes more electrical power than any other component in a conventional desktop or laptop computer. A significant portion of the electrical power consumed by the cpu is dissipated as heat during operation of the computer. Thus, the cpu tends to produce more heat than any other component within a computer system. A heat sink can be provided to increase the area of the cpu available for convective cooling and to redce the thermal resistance between the cpu and the ambient environment. Convective cooling enhanced by a heat sink may be sufficient in limited operating conditions. More generally, at least one dedicated cooling fan is provided to force ambient air across a cpu surface. In many cases another cooling fan is provided to move air across the surface of other components within the computer chassis.
Providing multiple fans introduces problems into the operation of a computer system. In many cases the operating life of a cooling fan is less than the projected operating life of the computer system. Providing multiple fans increases the probability of failure of a single fan. Failure of a fan can lead to failure of the computer system and decreased customer satisfaction.
U.S. Pat. No. 5,168,424 to Bolton et al. titled xe2x80x9cMulti Unit Electrical Apparatus with Dual Inlet Fan Positioned Opposite Unit Baysxe2x80x9d (also referred to as xe2x80x9cBoltonxe2x80x9d) teaches an electrical system having fans which can be dedicated to various components within the system. However, Bolton does not teach multiple fans dedicated to one component.
Multiple fans can also increase operating noise of a system. When both fans are operating they may interact, in some cases even operating at resonant frequency. Increased noise causes distraction and also causes decreased customer satisfaction. Multiple fans operating simultaneously can be cooling a component which requires cooling from only one fan, thus increasing manufacturing cost without benefit.
U.S. Pat. No. 5,687,079 to Bauer et al. titled xe2x80x9cMethod and Apparatus for Improved Control of Computer Cooling Fan Speedxe2x80x9d (also referred to as xe2x80x9cMossxe2x80x9d) teaches controlling fan speeds to prevent audible noise from being produced by the fans. However, Bauer does not teach alternating operation of cooling fans. Nor does Bauer teach controlling fan speeds in response to cpu temperature or internal temperature of a computer system.
U.S. Pat. No. 5,546,272 to Moss et al. titled xe2x80x9cSerial Fan Cooling Subsystem for Computer Systemsxe2x80x9d (also referred to as xe2x80x9cMossxe2x80x9d) teaches using fans in series to cool components of a computer system. However, Moss does not teach alternating operation of the fans to increase fan reliability. Nor does Moss teach varying the speed of a fan to increase fan reliability or to reduce noise.
U.S. patent application Ser. No. 09/537,159 filed on Mar. 29, 2000 listing Stephen J. Davies, Jil M. Bobbitt and Jason D. Tunnell as inventors, titled xe2x80x9cSeries Fan Speed Control System,xe2x80x9d now U.S. Pat. Ser. No. 6,396,688 (also referred to as xe2x80x9cDaviesxe2x80x9d) again teaches cooling a computer component using fans in series. Davies also teaches switching from one fan to another if a fan fails. However, Davies teaches two fans operating in series, not in parallel. However, in a series configuration if one fan fails the remaining fan must pull air through or push air past the disabled fan. Nor does Davies teach alternating fans to increase operating reliability of the system. Nor does Davies teach controlling fan speed to increase system reliability or reduce noise.
In accordance with the present disclosure an apparatus and a method are taught to increase the reliability of a computer system or other electronic system. A computer system includes a plurality of cooling fans configured to operate in parallel. The cooling fans are operated in a manner to increase the reliability of the fans. Thus the fans have an extended life. The increased life of the cooling fans increases the reliability of the system.
The cooling fans are operated in a manner to decrease the operating time of a fan. The cooling fans can alternate in operation. Thus, operating time is more equally divided between the two cooling fans and the hours of operation and number of rotations of the fans is more nearly equal. In an embodiment, a fan operates with a reduced speed which maintains a desired operating temperature. In an embodiment to reduce noise, two fans run at a lower speed instead of one fan at a higher speed. In an embodiment a thermal table is stored in BIOS (basic/input output system).
The foregoing is a summary and this contains, by necessity, simplifications, generalizations and omissions of detail; consequently, those skilled in the art will appreciate that the summary is illustrative only and is not intended to be in any way limiting.